/* p6_6.c: Toggle the red LED using the SysTick interrupt

 * This program sets up the SysTick to interrupt at 1 Hz.
 * The system clock is running at 41.94 MHz.
 * In the interrupt handler, the red LED is toggled.
 */

#include <MKL25Z4.H>

int main (void) {
    __disable_irq();            /* global disable IRQs */

    SIM->SCGC5 |= 0x400;        /* enable clock to Port B */
    PORTB->PCR[18] = 0x100;     /* make PTB18 pin as GPIO */
    PTB->PDDR |= 0x40000;       /* make PTB18 as output pin */
  
    SysTick->LOAD = 41940000/16-1; /* reload with number of clocks per second */
    SysTick->CTRL = 3;          /* enable SysTick interrupt, use system clock/16 */

    __enable_irq();             /* global enable interrupt */
    
    while (1) { /*wait here for interrupt */
    }
}

void SysTick_Handler(void) {
    PTB->PTOR = 0x40000;        /* toggle red LED */
}